Uniformly-shaped particulate resins can be used for various purposes such as electrophotographic toners, spacers for use in liquid crystal panels, colored particles for use in electronic papers, and carriers for medicines. Specific examples of the method for producing such uniformly-shaped particulate resins include methods in which a uniformly-shaped particulate resin is produced by making a reaction in a liquid, such as soap-free polymerization methods. Soap-free polymerization methods have advantages such that a particulate resin having a relatively small particle diameter and a sharp particle diameter distribution can be produced; and the particle form is nearly spherical, but have drawbacks such that a long time, and large amounts of water and energy are necessary for producing a particulate material because it takes time to perform such a polymerization reaction, it takes time to remove a solvent (typically water) from the liquid in which the reaction is performed, resulting in deterioration of production efficiency, and it is necessary to perform various processes such as a process for separating the resultant particulate material, and processes for washing and drying the particulate material after producing the particulate material in the liquid.
In attempting to solve the problems mentioned above, one of the present inventors and another inventor propose a toner production method using an ejection granulation method. Specifically, the toner production method uses a droplet ejection unit for ejecting droplets of a toner composition liquid including a solvent and toner components such as a binder resin and a colorant. The droplet ejection unit has a thin film, which has multiple nozzles and which is periodically vibrated up and down by an electromechanical converter serving as a vibrator to periodically change the pressure in a chamber, which contains the toner composition liquid and which includes the thin film having the multiple nozzles as a constitutional member, thereby ejecting droplets of the toner composition liquid from the nozzles to a space present below the nozzles. The thus ejected droplets of the toner composition liquid naturally fall through the space and proceed in the same direction, thereby forming lines of droplets of the toner composition liquid. In this regard, the ejected droplets are reshaped so as to be spherical due to the difference in surface tension between the toner component liquid and air in the space. The reshaped droplets are then dried, resulting in formation of a particulate toner.
In the toner production method, the falling speed of the ejected droplets decreases due to friction of air, and thereby the distance between a first droplet and a second droplet ejected after the first droplet gradually decreases, resulting in uniting of the droplets. Since the thus united droplets increase the volume thereof, the falling speed of the united droplets decreases due to friction of air, and therefore the united droplets tend to be further united with following droplets. Thus, there is a mixture of single droplets and united droplets in the space. When the mixture is dried, toner particles having different particle diameters are formed. Therefore, it is hard to form a uniformly-shaped particulate toner.
In attempting to solve the droplet uniting problem, one of the present inventors and other inventors propose a toner production method. In the toner production method, line of droplets of a toner composition liquid sequentially ejected from multiple nozzles are fed through a passage to a drying region, which is present on a downstream side of the space and in which the droplets are dried, and airflow is formed in the passage toward the drying region so that the droplets are fed by the airflow, to prevent uniting of the droplets.
In this toner production method, a large amount of air is supplied vertically from an entrance, which is located in the vicinity of droplet ejection nozzles, to the space by applying a pressure thereto using a pump or the like. In this regard, the pressure at the entrance is higher than that in peripheral areas in the space because the pressure of supplied air is added to the pressure of air used for ejecting droplets, and therefore the pressure in the peripheral areas decreases as the areas are apart in the lateral direction from the lines of droplets, resulting formation of pressure difference in the lateral direction in the space. Therefore, air supplied from the entrance is attracted by the peripheral areas, which have a low pressure, and then gradually spreads in the space. Accordingly, the lines of droplets are also spread by the airflow in the lateral direction, and a droplet in a line of droplets tends to be united with another droplet in the adjacent line of droplets before reaching the drying region.
In attempting to solve the droplet uniting problem, some of the present inventors and other inventors propose another toner production method. In the toner production method, air is supplied in the same direction as the droplet ejection direction to form a first airflow in the space, while air is supplied in a direction at an angle of less than 120° relative to the direction of the first airflow to form a second airflow in the space. In this case, the velocity of the droplets of the toner composition liquid is increased in the droplet ejection direction, but the velocity is gradually decreased. Therefore, the above-mentioned droplet spreading phenomenon is caused. In attempting to prevent occurrence of the droplet spreading phenomenon, the second airflow is supplied to each droplet at an angle of less than 120°. By supplying the second airflow, the feeding direction of the droplet is forcibly changed, and the distance between two adjacent droplets in the droplet feeding direction is increased, thereby preventing occurrence of the droplet uniting problem.
Since this toner production method uses two airflow generating devices, the costs of the toner production apparatus increase.
For these reasons, the inventors recognized that there is a need for a particulate material production method which can produce a uniformly-shaped particulate material at low costs without causing the droplet uniting problem.